The present invention relates generally to engine compression release brakes, and more particularly, to a method and apparatus of controlling the actuation of a compression brake.
Engine retarding devices of the compression release type may be utilized in machines such as on-highway trucks and the like. A compression release brake assembly utilizes compression within the machine""s engine to assist the machine""s main braking system in order to slow the machine. In effect, such compression release brake assemblies convert the machine""s internal combustion engine into an air compressor in order to develop retarding horsepower which is utilized to assist in slowing the machine.
Machine engines, such as truck engines, have physical speed limitations, which if exceeded, may cause the engine to fail. For example, if an engine, exceeds a particular speed, e.g., 2200 revolutions per minute, then the engine may fail. The particular speed which an engine may fail may vary from one engine to another, and from one engine size to another. The engine may fail, for example, because the crankshaft and therefore the associated camshafts are rotating so rapidly, leading to the opening and closing of the intake and exhaust valves occurring more rapidly and with increased force such that damage to the valves may occur, which may lead to additional damage to the cylinder and/or piston. In addition, piston lubrication begins to break down much quicker at high engine speeds, especially if the engine speed is maintained for a noticeable amount of time, thereby causing damage to the cylinder and/or piston.
Therefore, when a machine begins to travel downhill, for example, the engine speed may increase, even without an increase in throttle position. If the speed increases to much engine damage may occur. In addition, if the engine is downshifted, the engine speed may suddenly increase from an acceptable value in the previous gear, to an unacceptable value in the downshifted gear, causing engine damage to occur.
Some systems, such as that disclosed in U.S. Pat. No. 5,634,446, utilize a compression brake, or auxiliary brake, to maintain the speed of a vehicle during activation of a cruise control system. That is, when the cruise control system is engaged, the system monitors the speed and/or acceleration of the vehicle, and engages the auxiliary brake if necessary to maintain a desired vehicle speed. However these systems are inadequate to prevent engine overspeed conditions that may lead to failure. There may not inherently be a direct correlation between vehicle speed and engine speed. For example, in some situations, such as traveling downhill, engine speed may increase significantly without a corresponding increase in vehicle speed. Monitoring vehicle speed would not provide the necessary information to determine if the engine speed was above a desired speed. If the speed increases to much engine damage may occur. In addition, if the engine is downshifted, the engine speed may suddenly increase to an unacceptable value in the downshifted gear. The downshift may cause an unacceptable engine speed in the downshifted gear, without any change in vehicle speed.
The present invention is directed to overcoming one or more of the problems identified above.
In one aspect of the present invention, a method of controlling the speed of an engine is disclosed. The engine includes a plurality of cylinders, and a compression brake operable on one or more of the cylinders. The method includes the steps of determining a speed of the engine, comparing the engine speed to a first threshold, and activating the compression brake for at least one of said cylinders in response to the engine speed exceeding the first threshold.
In another aspect of the present invention, an apparatus configured to control the speed of an engine is disclosed. The engine includes a plurality of cylinders, and the apparatus includes a compression brake operable one or more of the cylinders of the engine. The apparatus comprises a speed sensor adapted to sense an engine characteristic indicative of an engine speed and responsively generate an engine speed signal, and a controller configured to receive said engine speed signal, compare the engine speed to a first threshold, and activate the compression brake for at least one of the cylinders in response said engine speed exceeding the first threshold.